Ferrofluids are typically a colloidal dispersion of very finely-divided magnetic particles dispersed in a liquid, and are used, for example, in the construction of modular magnetic fluid seals and bearings (see, for example, U.S. Pat. No. 3,620,584, issued Nov. 16, 1971; U.S. Pat. No. 3,917,538, issued Nov. 4, 1975; and U.S. Pat. No. 3,977,739, issued Aug. 31, 1976 (all hereby incorporated by reference herein).
Ferrolubricants are a particular class of ferrofluids, wherein the liquid performs a lubricating function; that is, magnetizable lubricants that can be controlled and held in place by magnetic means. Ferrolubricants were developed because users of rotating and sliding mechanisms have always experienced problems in retaining lubricants at the critical wear or contact points.
Liquids, such as oil; for example, hydrocarbons, esters, silicones, etc., are the ideal lubricants; however, they do not tend to stay at or within the critical areas. It is even difficult to maintain them within the confines of the mechanism due to creep, gravity, centrifugation or other forces, generally leading to oil migration. When the oil migrates, the quantity left in the assembly or mechanism is reduced, thereby potentially reducing the life of the assembly. Another problem created by migration is contamination of adjacent areas where the oil is not desired, such as electrical connections, lenses, armatures, slip rings, etc.
Designers and engineers have attempted to overcome migration problems by using higher viscosity materials, commonly greases. Greases eliminate the contamination of adjacent areas due to migration, but often create new problems due to their high viscosity. For example, when used in rotating or sliding mechanisms, more torque is required to start and move the mechanism. The torque requirement does not remain constant in that grease, when left static, tends to take a set, resulting in high-starting torque. In addition, temperature increases often result when mechanical movement commences. This thermal increase in many cases will be high enough to deteriorate the lubricating properties of the grease. Also, the thermal increase changes the lubricant's viscosity, resulting in changing torque requirements which are very undesirable in precision mechanisms.
A lip seal is intended to provide a dynamic barrier about a rotating shaft which resists passage of contaminants (solid, liquid or gaseous) into the region which the lip seal is protecting. The lip seal may provide protection and separation of different environments at the same pressure or at different pressures, with the same or different environments. The lip seal provides protection by maintaining contact with the shaft as intimately as possible. This contact, however, is by no means hermetic, and, in fact, degrades in and with use by various mechanisms. When the seal is installed, it is usually provided with a coating of lubricant oil or grease. When the shaft rotates, this lubricant is then discharged from the contact area due to contact forces, centrifugation, heat (resulting in vaporization of the liquid lubricant), creep, gravity or migration caused by surface-energy phenomena. If the lubricant is not reapplied, the seal element breaks down due to heat of friction caused by rubbing, entrapment of abrasive particulate contamination in the contact region, or chemical reaction of the environment with the elastomer. Thus, improvements in dynamic lip seals are desirable to improve the sealing function of the seal, to retain lubricants in place, and to improve the use life of the seal.